The present invention relates to a hydraulic system for controlling movement of the boom and bucket of an end loader.
Various hydraulic systems have heretofore been made for controlling the boom and bucket of an end loader. In the system disclosed in U.S. Pat. No. 3,563,137, fluid exiting from the rod end of the boom cylinder during raising of the boom, passes through a valve type flow divider that dumps a portion to drain while directing the remaining portion to the piston end of the bucket cylinder to level the bucket during raising of the boom. In one embodiment of this patent, the boom control valve was modified to provide a boom-raise and level position and boom-lower and level position, in addition to the customary boom-raise and boom-lower positions. The boom control valve was operative in the boom-lower and level position to pass fluid exiting from the piston end of the boom cylinder during lowering of the boom through a second valve type flow divider arranged to direct one portion of the inlet flow to the rod end of the bucket cylinder and to dump the remaining portion to drain.
Valve type flow dividers divide flow from an inlet into separate streams at two outlets in accordance with the pressure drop through two orifices and can operate reliably only when the pressure at the inlet is substantially greater than the pressure at either outlet. During lowering of the boom, a portion of the fluid from the piston end of the boom cylinder is passed to the rod end of the bucket cylinder. The area of the piston end of the boom cylinder is usually very large as compared to area of the rod end of the bucket cylinder and it has been found that, under some operating conditions, the pressure at the piston end of the boom cylinder is too low as compared to the pressure required at the rod end of the bucket cylinder, to reliably move the bucket when the latter is loaded. Further, in the bucket level system in U.S. Pat. No. 3,563,137, the flow fluid divider valve was arranged to dump a portion of fluid to drain and could not be used with series connected boom and bucket control valves.
U.S. Pat. Nos. 4,408,518; 4,561,342; 4,709,618 and 4,723,478 disclose boom and bucket control systems having a flow divider valve to control bucket leveling during raising of the boom and which are suitable with series connected control valves and parallel connected control valves. However, the systems disclosed in the above patents were not operative to control leveling of the bucket during lowering of the boom.